The term “transverse gradient” (also known as a “cross slope” in Switzerland) in highway and roadway construction refers to the inclination of the road surface (or a layer beneath same) in a direction at a right angle to the axis of the road.
Transverse gradient q is usually given in percentage. For example, a 1% transverse gradient corresponds to a height difference of 1 cm per 1 m. The main purpose of a transverse gradient is the rapid and harmless runoff of surface water to protect the body of the road from moisture and to prevent accumulations of water and the consequences thereof (aquaplaning, formation of a spray mist or black ice). However, the transverse gradient also fulfills the purposes of driving dynamics, such as absorbing, i.e., reducing the centrifugal force when driving fast through curves, for example. The transverse gradient also provides visual guidance for the driver, thereby improving perception of the curve.
Modern antilock braking systems (ABS) and integral braking systems on two-wheelers are well-developed and reliable in so-called straight-ahead braking actions and braking actions at a moderate tilt. At a greater tilt, the parameters of the braking system (for example, braking force distribution, brake pressure gradient and control strategy) must be adapted while negotiating a curve in order to ensure safe braking again in this situation. Knowledge of the tilt of the two-wheeler is essential for this. However, adaptive headlight systems, chassis systems and vehicle dynamics control systems require at least the tilt as an input variable.
A braking action while negotiating a curve results in a two-wheeler in a steering torque in the direction of the inside of the curve due to the geometric conditions. This steering torque creates a so-called righting moment. To at least diminish this, therefore, steering assistance systems may be provided to exert a steering momentum on the steering as a function of the braking intensity. The steering momentum is directed toward the outside of the curve. it counteracts the righting moment. Here again, at least the tilt must be known.
As indicated in DE 10 2007 061 114 A1 and DE 10 2011 076 640 A1, for example, the tilt may be ascertained using a tilt sensor. However, known tilt sensors measure the tilt of a two-wheeler only relative to the horizontal or vertical. However, the transverse gradient of the road surface is not taken into account.
However, the inclination of the two-wheeler relative to the road surface is also crucial for the transferable force during acceleration or braking. For example, it is possible to accelerate more in a curve, which is inclined more in the direction of the inside of the curve, than in a curve whose transverse gradient is directed less outwardly or not at all.
There is therefore a need for improvements taking into account the transverse gradient in the aforementioned application cases involving two-wheelers.